It is known to provide a lash free axially collapsible steering column by providing a plurality of spring loaded members located in one of the shafts which abut polygonal surfaces of the other shaft to eliminate torsional lash therebetween. This spring loading can be by spring loaded balls, or by utilizing a coil spring, a rubber block or other resilient member in a blind bore behind a ball or cylindrical roller.
In Australian Pat. No. 429,180 the lash is eliminated by balls press-fitted into corresponding bores in one of the shafts, there being provided a rotationally flexible section between these balls and a fail-safe portion, which fail-safe portion becomes operative at torque levels above a predetermined value.
The embodiments also show examples where either the inner hex shaft is twisted or the outer tube is twisted to provide a pre-load, there still being provided a torsional fail-safe portion in the inner hex shaft.
However, with the invention to Australian Pat. No. 429,180 it is apparent that due to the hex shaft, and the outer tube of corresponding shape that the load applied is virtually a point loading at the apices of the hex shaft.
In order to eliminate indentation of the tube and/or rounding or other deforming of the apices of the hex shaft the torsional fail shaft portion is required which then transfers the torque to the other end of the hex shaft where the excess torque is transmitted.
It is an object of this invention to provide a lash axially adjustable steering column in which the column is simple and economic to produce and which does not require a fail-safe portion.